1. Field of the Invention
The present invention relates to a gas discharge tube; and, more particularly, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like.
2. Related Background Art
As a conventional technique of this field, one disclosed in Japanese Patent Laid-Open No. 7-326324 is available. As shown in FIG. 9, a gas discharge tube (deuterium lamp) 100 described in this reference has a glass sealing envelope 101, and a light emitting part assembly 102 is held in the sealing envelope 101 in a floating state. The light emitting part assembly 102 is comprised of an anode plate 105 sandwiched by ceramic support plates 103 and 104, a cathode section 106 located above the anode plate 105, and a converging electrode plate 107 arranged between the anode plate 105 and cathode section 106. To use this discharge lamp, a predetermined voltage is applied to the anode plate 105, cathode section 106, and converging electrode plate 107 to cause arc discharge above a converging opening 107a of the converging electrode plate 107, and light generated by arc discharge is emitted outside through a light projecting window 101a of the sealing envelope 101. Emitted light is guided to an optical system for focusing the light or transmitting it through a fine slit. In order to increase the light use efficiency, a portion having the highest light intensity, i.e., the emission central point, must be set on the optical path. The lamp 100 must be reliably set at a predetermined position of a lamphouse 108 and the emission central point must be accurately positioned. For this purpose, in this conventional apparatus, a flange member 109 as a separate component is fixed to the lamp 100 through an adhesive R, so that the lamp 100 can easily be set in a lamp accommodating recess 110 of the lamphouse 108. To fix the flange member 109 by adhesion, the flange member 109 is aligned with the emission central point of the lamp 100 while observing it, and the flange member 109 is fixed to the outer surface of the sealing envelope 101. When setting the lamp 100 in the lamphouse 108, set screws 111 provided in the lamp accommodating recess 110 are inserted through screw insertion holes 112 in the flange member 109, and the lamp 100 is fixed to the lamphouse 108 by using the set screws 111 and nuts 113. Stem pins 114 of the lamp 100 are inserted in a socket 115, thereby setting the lamp 100. Hence, the emission central point can be arranged on a predetermined optical path.
The conventional gas discharge tube described above suffers the following problems. The flange member 109 is a component separate with respect to the lamp 100, and is fixed to the lamp 100 through the adhesive R. As a result, the positional relationship between the flange member 109 and the emission central point of the lamp 100 may undesirably change while the adhesive R is set. It takes time to adhere the flange member 109. Even if the emission central point and the flange member 109 of the lamp 100 are precisely aligned with each other, when setting the lamp 100 in the lamp accommodating recess 110, the screw insertion holes 112 are not suitable for high-precision alignment as they are holes in which the set screws 111 are to be inserted. Alignment of the emission central point of the lamp 100 must accordingly be performed depending on the skill of the operator or a predetermined adjusting jig. Therefore, the lamp 100 cannot be positioned in the lamp accommodating recess 110 easily and reliably at high precision.
The present invention has been made to solve the above problems, and has as its object to provide a gas discharge tube in which an assembling workability and an attaching precision with respect to an optical system are improved.
In order to solve the above problems, according to the present invention, there is provided a gas discharge tube in which a gas is sealed in a sealing envelope at least part of which can transmit light, and discharge is caused between an anode section and a cathode section arranged in the sealing envelope, so that predetermined light is emitted through a light transmitting portion of the sealing envelope. This sealing envelope comprises a stem for securing the cathode and anode sections by way of respective stem pins independent from each other, and a side tube, at least part of which is made of a light transmitting material, surrounding the cathode and anode sections and being joined to the stem. Wherein the stem has an integrally formed flange portion extending in a direction perpendicular to an axial direction of the side tube and having a positioning reference portion when attaching the gas discharge tube to an external fixing member.
In this gas discharge tube, since the flange portion is integrally formed with the stem, operation for constructing and fixing the flange portion is not necessary when assembling the lamp, so that lamp assembly operation is simplified, and mass production is facilitated. In addition, since the positioning reference portion is positively formed on the flange portion integrated with the stem, lamp setting is enabled at higher precision.
The gas discharge tube preferably further comprises an anode support plate in contact with a surface of the stem which is inside the sealing envelope, and supporting the anode section on an opposite surface thereof, a ceramic spacer in contact with an exposed surface of the anode support plate and having an opening for exposing the anode section therethrough, and a converging electrode plate in contact with the exposed surface of the spacer to oppose the anode section and having a converging opening coaxial with the opening of the spacer, the converging electrode plate being made of a conductive member.
When this arrangement is employed, since the stem, the anode support plate, the spacer, and the converging electrode plate are stacked to be in contact with each other, heat generated by the anode section or converging electrode plate can be radiated outside through the stem 4. Hence, the stem functions as a heat sink. In assembly, the positional relationship between the stem and the converging electrode plate can be regulated at high precision with the simple assembly operation of stacking the respective constituent members on the stem. This contributes to alignment of the emission central point with the flange portion integrated with the stem.
The positioning portion preferably has a positioning hole or notch for inserting a positioning pin inserted another end in a positioning hole formed in a stem setting portion of an external fixing member where the gas discharge tube is to be attached, or a positioning pin standing upright from the stem setting portion. In this case, positioning that keeps a relationship between the pin and hole is enabled, and setting is enabled at high precision by a simple structure in which merely a positioning pin, a positioning hole, or a notch portion is formed in the flange portion.
Alternatively, the positioning portion preferably has a projecting portion projecting from the flange portion laterally or a cut-off portion formed on an outer surface of the flange portion so as to conform to a shape of a stem setting portion of the external fixing member to which the gas discharge tube is to be mounted. Alternatively, the flange portion may have an outer shape of a predetermined polygon. In this case, the outer shape of the flange portion itself is a characteristic feature. As a result, the flange portion can cope with use situations in various manners with the shape of the projecting portion or the cut-off portion, or by changing its outer diameter itself, so that lamp setting is enabled at high precision with a simple arrangement.
The present invention can be understood more sufficiently through the detailed description and accompanying drawings which follow. Note that the detailed description and accompanying drawings are shown merely for illustrative examples and should not be construed to limit the present invention.
Further application of the present invention will become apparent from the following detailed invention. Although the detailed description and specific examples show preferable embodiments of the present invention, they are shown merely for illustrative examples. Various modifications and improvements in the spirit and scope of the present invention are naturally apparent to one skilled in the art from the detailed description.